The blood coagulation cascade is an exquisite example of a responsive self-assembly process. When a wound if formed, a cascade of events is initiated. The net result of the cascade is an assembly of the globular protein fibrinogen, which is catalyzed by a second protein, thrombin, to yield chains of fibrin. A network of insoluble fibrin chains forms the hemostatic “plug” or clot, which presents a physical barrier to the loss of blood from the wound.
The coagulation cascade is a delicately balanced series of events; if it occurs too easily, blood clots may form in unwanted areas, leading to strokes or other complications. It is, however, possible to harness the clotting power of fibrin to create haemostatic dressing or bandages. There is a vital need for haemostatic dressings that can staunch the bleeding from serious trauma.
A wide variety of compositions and devices have been developed for use in controlling bleeding. However, available compositions and dressings typically have only a modest hemostatic effect, so that bleeding continues for several (e.g., 2-3 minutes or more) after application of composition or dressing. Additionally, many dressings have only modest antiseptic abilities. Also, typical dressings are prepared from materials that have a tendency to adhere to the injured surface, causing significant pain to the patient when the dressing is applied or removed. Because of the modest hemostatic and/or antiseptic activity, standard dressings often need to be changed frequently, further exacerbating adhesion problems.
Massive hemorrhaging, and particularly arterial bleeding, from severe trauma remains extremely difficult to control and treat. Advanced wound dressing are frequently employed in battlefield and emergency situations, but the results have been mixed. The HemCon® bandage, made from a chitosan derived from shrimp shells, was approved by the Pentagon's advisory committee on combat medicine in 2003 as the preferred dressing for combat. However, animal studies have shown that HemCon® is no more effective than gauze, and in certain circumstances even less effective. The bandage also proved less than effective in battlefield situations where it proved too small and rigid for battlefield injuries, rendering it extremely difficult to use on extremities.
Another advanced battlefield wound dressing, WoundStat®, has also proven inadequate, and has further been linked with potentially deadly complications in animal studies. The bandages are comprised in part of clay-like kaolin, which has been hypothesized to facilitate coagulation and clotting. However, in the particular WoundStat formulation, the kaolin can break loose and drift into veins and arteries, potentially causing deadly clots intraarterial and intravascular clots.